Communication control method

ABSTRACT

A base station and method thereof includes transmitting from the base station to a user equipment, parameters for an offload from the cellular RAN to a wireless local area network (LAN). The parameters are used by the user equipment to perform an access network selection between the cellular RAN and the wireless LAN, and include a first threshold for comparison with a cellular signal strength of the cellular RAN, a second threshold for comparison with a wireless LAN signal strength of the wireless LAN, and a third threshold for comparison with a load of the wireless LAN. When performing access network selection, the parameters may cause the user equipment to perform the offload, in response to the cellular signal strength being lower than the first threshold, the wireless LAN signal strength being higher than the second threshold, and the load of the wireless LAN being lower than the third threshold.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/650,620 filed Jul. 14, 2017, which is aContinuation Application of U.S. patent application Ser. No. 14/761,873filed Jul. 17, 2015, which is the U.S. National Phase Application ofInternational Patent Application No. PCT/JP2014/050836 filed Jan. 17,2014, which claims benefit of U.S. Provisional Application No.61/864,206 filed Aug. 9, 2013 and U.S. Provisional Application No.61/754,106 filed on Jan. 18, 2013, the entire contents of which areincorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a user terminal, chipset for a userterminal, and method performed at a user terminal for interworking acellular communication system with a wireless LAN system.

RELATED ART

In recent years, a user terminal including a cellular communication unitand a wireless LAN communication unit (so-called dual terminal) isbecoming widely used. Further, the number of wireless LAN access pointsoperated by an operator of a cellular communication system increases.

Therefore, 3GPP (3rd Generation Partnership Project), which is a projectaiming to standardize a cellular communication system, plans to considera technology capable of strengthening interworking between a cellularcommunication system and a wireless LAN system (see Non-patent document1).

CITATION LIST Non-Patent Document

-   [Non-patent document 1] 3GPP contribution RP-1201455

SUMMARY

When the interworking between the cellular communication system and thewireless LAN system is strengthened, it is possible to disperse a loadof the cellular communication system to the wireless LAN system.

Therefore, the present disclosure provides a user terminal, a chipsetfor a user terminal, and a method performed at a user terminal capableof strengthening an interworking between a cellular communication systemand a wireless LAN system.

A base station according to the present disclosure, which is included ina cellular radio access network (RAN), comprises a transmitterconfigured to transmit, to a user equipment, parameters for an offloadfrom the cellular RAN to a wireless local area network (LAN). Theparameters are used by the user equipment to perform an access networkselection between the cellular RAN and the wireless LAN, and include afirst threshold to be compared with a cellular signal strength of thecellular RAN, a second threshold to be compared with a wireless LANsignal strength of the wireless LAN, and a third threshold to becompared with a load of the wireless LAN.

In accordance with another exemplary aspect of the present disclosure,when the user equipment performs the access network selection, theparameters may cause the user equipment to perform the offload, inresponse to the cellular signal strength being lower than the firstthreshold, the wireless LAN signal strength being higher than the secondthreshold, and the load of the wireless LAN being lower than the thirdthreshold.

A method according to the present disclosure, which is performed at abase station included in a cellular radio access network (RAN),comprises transmitting, to a user equipment, parameters for an offloadfrom the cellular RAN to a wireless local area network (LAN). Theparameters are used by the user equipment to perform an access networkselection between the cellular RAN and the wireless LAN, and include afirst threshold to be compared with a cellular signal strength of thecellular RAN, a second threshold to be compared with a wireless LANsignal strength of the wireless LAN, and a third threshold to becompared with a load of the wireless LAN.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram according to a first embodimentto a ninth embodiment.

FIG. 2 is a block diagram of UE (user terminal) according to the firstembodiment to the ninth embodiment.

FIG. 3 is a block diagram of eNB (cellular base station) according tothe first embodiment to the ninth embodiment.

FIG. 4 is a block diagram of AP (wireless LAN access point) according tothe first embodiment and the second embodiment and the sixth embodimentto the ninth embodiment.

FIG. 5 is a protocol stack diagram of a radio interface in the LTEsystem.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem.

FIG. 7 is a diagram for illustrating an operation environment accordingto the first embodiment to the ninth embodiment.

FIG. 8 is a sequence diagram of an operation pattern 1 according to thefirst embodiment.

FIG. 9 is a sequence diagram of an operation pattern 2 according to thefirst embodiment.

FIG. 10 is a sequence diagram of an operation pattern 1 according to thesecond embodiment.

FIG. 11 is a sequence diagram of an operation pattern 2 according to thesecond embodiment.

FIG. 12 is a sequence diagram of an operation pattern 3 according to thesecond embodiment.

FIG. 13 is a block diagram of AP (wireless LAN access point) accordingto the third embodiment to the fifth embodiment.

FIG. 14 is a block diagram of a small cell eNB according to the thirdembodiment.

FIG. 15 is a diagram for illustrating an operation according to thethird embodiment.

FIG. 16 is a sequence diagram of an operation pattern 1 according to thethird embodiment.

FIG. 17 is sequence diagram of an operation pattern 2 according to thethird embodiment.

FIG. 18 is a diagram for illustrating an operation according to a thirdembodiment.

FIG. 19 is a diagram for illustrating an operation according to thethird embodiment.

FIG. 20 is a sequence diagram according to the fourth embodiment.

FIG. 21 is a sequence diagram of an operation pattern 1 according to thefifth embodiment.

FIG. 22 is a sequence diagram of an operation pattern 2 according to thefifth embodiment.

FIG. 23 is a sequence diagram according to the sixth embodiment.

FIG. 24 is sequence diagram of an operation pattern 1 according to theseventh embodiment.

FIG. 25 is a sequence diagram of an operation pattern 2 according to theseventh embodiment.

FIG. 26 is a sequence diagram of an operation pattern 1 according to theeighth embodiment.

FIG. 27 is a sequence diagram of an operation pattern 2 according to theeighth embodiment.

FIG. 28 is a sequence diagram according to the ninth embodiment.

FIG. 29 is a diagram for illustrating an operation according to otherembodiments.

DETAILED DESCRIPTION OF EMBODIMENTS Overview of Embodiment

A communication control method according to a first embodiment is amethod for performing an offload from a cellular RAN to a wireless LAN.The communication control method includes the steps of: transmitting alist which contains identifiers of wireless LAN access points includedin the wireless LAN, by a cellular base station included in the cellularRAN; receiving the list, by a user terminal which has a cellularcommunication unit and a wireless LAN communication unit; and performingan operation related to the offload after detecting that the userterminal approaches a wireless LAN access point on the basis of thelist, by the user terminal which exists in a cell of the cellular basestation. Here, “detecting approaching” means “recognition ofapproaching”, and may mean not actually approaching (in case ofmisdetection). The same applies, below.

In the first embodiment, in the step of performing the operation relatedto the offload, the user terminal, in which the wireless LANcommunication unit is in an OFF state, scans the wireless LAN accesspoint by switching the wireless LAN communication unit to an ON state,after detecting that the user terminal approaches the wireless LANaccess point on the basis of the list.

In the first embodiment, the operation comprises a scan for the wirelessLAN access point. The communication control method further comprises astep of transmitting a notification indicating that the wireless LANaccess point has been discovered, from the user terminal to the cellularbase station, when the wireless LAN access point has been discovered bythe scan.

In the first embodiment, the notification includes an identifier of thewireless LAN access point that has been discovered. The communicationcontrol method further comprises a starting up step of starting up thewireless LAN access point, by the cellular base station, when thecellular base station receives the notification and the wireless LANaccess point corresponding to the identifier included in thenotification is in an OFF state.

In the first embodiment, in the step of transmitting, the cellular basestation transmits the list to the user terminal on the basis of a loadlevel regarding the cellular base station.

In the first embodiment, the communication control method furtherincludes a step of determining whether or not to use the list on thebasis of status of the user terminal, by the user terminal.

In the first embodiment, the list contains identifiers of wireless LANaccess points provided within a cell of the cellular base station oridentifiers of wireless LAN access points provided within a trackingarea including the cell.

A communication control method according to second and seventhembodiments is a method for performing an offload from a cellular RAN toa wireless LAN. The communication control method includes the steps of:transmitting information for the offload, by a cellular base stationincluded in the cellular RAN; receiving the information from thecellular base station, by a user terminal which has a cellularcommunication unit and a wireless LAN communication unit and whichexists in a cell of the cellular base station; performing an operationrelated to the offload on the basis of the information received from thecellular base station, by the user terminal.

In the second and seventh embodiments, in the step of performing theoperation, the user terminal scans a wireless LAN access point byswitching the wireless LAN communication unit to an ON state on thebasis of the information received from the cellular base station, whenthe wireless LAN communication unit is in an OFF state.

In the second and seventh embodiments, in the step of transmitting, thecellular base station transmits the information to one or more userterminals when a load level of the cellular base station exceeds athreshold.

In the second and seventh embodiments, the communication control methodfurther includes a step of transmitting a notification indicating thatthe wireless LAN access point has been discovered, from the userterminal to the cellular base station, when the wireless LAN accesspoint has been discovered by the scan.

In the second and seventh embodiments, the information is informationinstructing to switch the wireless LAN communication unit to an ONstate.

In the second and seventh embodiments, the information includes locationinformation indicating a location of the wireless LAN access point. Inthe step of performing the operation, the user terminal performs theoperation when detecting, on the basis of the location information, thatthe user terminal approaches the wireless LAN access point.

In the second and seventh embodiments, the information includescondition information indicating a condition under which to perform theoperation. In the step of performing the operation, the user terminalperforms the operation when detecting, on the basis of the conditioninformation, that the condition is satisfied.

In the second and seventh embodiments, the information includesparameters to be applied to the operation.

In the second and seventh embodiments, the communication control methodfurther includes a step of determining whether to transmit theinformation to the user terminal on the basis of a status of the userterminal, by the cellular base station.

A communication control method according to a third embodiment includesthe steps of: broadcasting, by a specific apparatus cooperating with acellular base station, a discovery signal for informing of presence ofthe specific apparatus in a cellular frequency band and in a specificperiod; and scanning, by a user terminal connecting to the cellular basestation, the discovery signal in the cellular frequency band and in thespecific period.

In the third embodiment, the specific period is designated by thecellular base station.

In the third embodiment, the specific apparatus is an apparatus thatperforms communication outside the cellular frequency band.

In the third embodiment, the cellular base station is a base stationwhich performs communications at a first frequency within the cellularfrequency band. The specific apparatus is an apparatus which performscommunications at a second frequency within the cellular frequency band.In the step of broadcasting, the specific apparatus broadcasts thediscovery signal at the first frequency within the cellular frequencyband and in the specific period. In the step of scanning, the userterminal scans the discovery signal at the first frequency within thecellular frequency band and in the specific period.

In the third embodiment, the discovery signal includes an identifier ofthe specific apparatus.

In the third embodiment, the communication control method furtherincludes a step of transmitting a discovery notification indicating thatthe discovery signal is detected, from the user terminal to the cellularbase station, when the user terminal detects the discovery signal by thescan.

In the third embodiment, the communication control method furtherincludes a step of transmitting a connection notification indicatingthat the user terminal is connected to the specific apparatus, from thespecific apparatus to the cellular base station, when the user terminalconnects to the specific apparatus after detecting the discovery signalby the scan.

In the third embodiment, the specific apparatus is a wireless LAN accesspoint.

In the third embodiment, the specific apparatus is a cellular basestation that manages a small cell.

In the third embodiment, the specific apparatus is another user terminalthat supports inter-terminal radio communications.

In the third embodiment, the cellular frequency band is included in alicensed band. The specific apparatus is another cellular base stationwhich performs communications in an unlicensed band.

A communication control method according to fourth embodiment includesthe steps of: receiving a cellular reference signal broadcasted from aspecific apparatus within a cellular frequency band included in alicensed band, by a user terminal connected to a cellular base station;reporting measurement information indicating a measurement result forthe cellular reference signal, from the user terminal to the cellularbase station; and transmitting information for scanning the specificapparatus to the user terminal, on the basis of the measurementinformation reported from the user terminal, by the cellular basestation. The specific apparatus is an apparatus which performscommunications in an unlicensed band.

In the fourth embodiment, a cell identifier for identifying the specificapparatus is assigned to the specific apparatus. The cellular referencesignal transmitted by the specific apparatus includes the cellidentifier.

A communication control method according to a fifth embodiment includesthe steps of: detecting a cellular uplink signal transmitted by a userterminal connected to a cellular base station, by a specific apparatus;transmitting a notification indicating that the user terminal approachesthe specific apparatus on the basis of the detection of the cellularuplink signal, from the specific apparatus to the cellular base station;and transmitting information for scanning the specific apparatus on thebasis of the notification from the specific apparatus, from the cellularbase station to the user terminal.

In the fifth embodiment, the communication control method furtherincludes a step of determining whether or not the user terminalapproaches the specific apparatus, by the specific apparatus. The stepof determining comprises the steps of: acquiring signal information on acellular uplink signal transmitted by the user terminal, from thecellular base station, estimating a pathloss between the user terminaland the specific apparatus on the basis of the signal information; anddetermining that the user terminal approaches the specific apparatuswhen the pathloss is less than a threshold.

In the fifth embodiment, the communication control method furtherincludes a step of determining, by the specific apparatus, whether ornot the user terminal approaches the specific apparatus on the basis ofa distance between the specific apparatus and the cellular base stationand a received power of the cellular uplink signal.

A communication control method according to a sixth embodiment includes:a deriving step of deriving a moving velocity of a user terminal havinga cellular communication unit and a wireless LAN communication unit andbeing connected to a cellular base station, by the user terminal; and asuspension step of suspending a scan for the wireless LAN access pointwhen the moving velocity exceeds a threshold even if the wireless LANcommunication unit is in an ON state, by the user terminal.

A communication control method according to an eighth embodimentincludes the steps of: transmitting notification information indicatinga switch from a specific apparatus to a cellular base station, from auser terminal to the cellular base station, when the user terminalswitches a connection target from the specific apparatus to the cellularbase station; and transmitting, from the cellular base station to thespecific apparatus, request information requesting to transfertransmission data addressed to the user terminal to the cellular basestation on the basis of the notification information. The specificapparatus is an apparatus which performs communications in an unlicensedband.

In the eighth embodiment, the notification information includes anidentifier for identifying the specific apparatus.

In the eighth embodiment, the notification information includes anidentifier for identifying the user terminal.

A communication control method according to a ninth embodiment includesthe steps of: deciding, by a specific apparatus arranged within acoverage of a cellular base station, to switch a connection target of auser terminal from the specific apparatus to the cellular base station,without receiving a measurement report about the cellular base stationfrom the user terminal; transmitting, from the specific apparatus to thecellular base station, request information requesting a switch to thecellular base station; and transmitting, from the specific apparatus tothe user terminal, instruction information for instructing a switch tothe cellular base station when the specific apparatus receives, from thecellular base station, a response for the request information. Thespecific apparatus is an apparatus which performs communications in anunlicensed band.

Below, with reference to the drawing, each embodiment will be describedin which an LTE system that is a cellular communication systemconfigured in compliance with the 3GPP standards is interworked with awireless LAN (WLAN) system.

First Embodiment

(System Configuration According to First Embodiment)

FIG. 1 is a system configuration diagram according to a firstembodiment. As illustrated in FIG. 1, the LTE system includes aplurality of UEs (User Equipments) 100, E-UTRAN (Evolved-UMTSTerrestrial Radio Access Network) 10, and EPC (Evolved Packet Core) 20.E-UTRAN 10 corresponds to a radio access network. The EPC 20 correspondsto a core network.

The UE 100 is a mobile radio communication device and performs radiocommunication with a cell with which a connection is established. The UE100 corresponds to the user terminal. The UE 100 is a terminal (dualterminal) that supports both cellular communication and WLANcommunication.

The E-UTRAN 10 includes a plurality of eNBs 200 (evolved Node-Bs). TheeNB 200 corresponds to a base station. The eNB 200 manages one or aplurality of cells and performs radio communication with the UE 100which establishes a connection with the cell of the eNB 200. It is notedthat the “cell” is used as a term indicating a minimum unit of a radiocommunication area, and is also used as a term indicating a function ofperforming radio communication with the UE 100. Further, the eNB 200,for example, has a radio resource management (RRM) function, a routingfunction of user data, and a measurement control function for mobilitycontrol and scheduling.

The eNBs 200 are connected mutually via an X2 interface. Further, theeNB 200 is connected to MME/S-GW 500 included in the EPC 20 via an S1interface.

The EPC 20 includes a plurality of MMEs (Mobility ManagementEntity)/S-GWs (Serving-Gateways) 500. The MME is a network node forperforming various mobility controls, for example, for the UE 100 andcorresponds to a controller. The S-GW is a network node that performstransfer control of user data and corresponds to a mobile switchingcenter.

The WLAN system includes WLAN AP (hereinafter, “AP”) 300. The WLANsystem is configured to be in compliance with various IEEE 802.11specifications, for example. The AP 300 communicates with the UE 100 ina frequency band (WLAN frequency band) different from a cellularfrequency band. The AP 300 is connected to the EPC 20 via a router, etc.In the first embodiment, the AP 300 is operated by an operator of acellular communication system (LTE system). Note that the cellularfrequency band is included in a licensed band (frequency band for whicha license is required). On the other hand, the WLAN frequency band isincluded in an unlicensed band (frequency band for which a license isnot required).

Subsequently, configurations of the UE 100, the eNB 200, and the AP 300will be described.

FIG. 2 is a block diagram of the UE 100. As shown in FIG. 2, the UE 100includes: antennas 101 and 102; a cellular transceiver (cellularcommunication unit) 111; a WLAN transceiver (WLAN communication unit)112; a user interface 120; a GNSS (Global Navigation Satellite System)receiver 130; a battery 140; a memory 150; and a processor 160. Thememory 150 and the processor 160 configure a control unit. The UE 100may not have the GNSS receiver 130. Furthermore, the memory 150 may beintegrally formed with the processor 160, and this set (that is, achipset) may be called a processor 160′.

The antenna 101 and the cellular transceiver 111 are used fortransmitting and receiving a cellular radio signal. The cellulartransceiver 111 converts a baseband signal output from the processor 160into the cellular radio signal, and transmits the same from the antenna101. Further, the cellular transceiver 111 converts the cellular radiosignal received by the antenna 101 into the baseband signal, and outputsthe same to the processor 160.

The antenna 102 and the WLAN transceiver 112 are used for transmittingand receiving a WLAN radio signal. The WLAN transceiver 112 converts thebaseband signal output from the processor 160 into a WLAN radio signal,and transmits the same from the antenna 102. Further, the WLANtransceiver 112 converts the WLAN radio signal received by the antenna102 into a baseband signal, and outputs the same to the processor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, andvarious buttons. Upon receipt of the input from a user, the userinterface 120 outputs a signal indicating a content of the input to theprocessor 160. The GNSS receiver 130 receives a GNSS signal in order toobtain location information indicating a geographical location of the UE100, and outputs the received signal to the processor 160. The battery140 accumulates a power to be supplied to each block of the UE 100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160. The processor160 includes the baseband processor that performs modulation anddemodulation, and encoding and decoding of the baseband signal and a CPUthat performs various processes by executing the program stored in thememory 150. The processor 160 may further include a codec that performsencoding and decoding of sound and video signals. The processor 160implements various processes and various communication protocolsdescribed later.

FIG. 3 is a block diagram of the eNB 200. As shown in FIG. 3, the eNB200 includes an antenna 201, a cellular transceiver 210, a networkinterface 220, a memory 230, and a processor 240. The memory 230 and theprocessor 240 configure a control unit. Furthermore, the memory 230 maybe integrally formed with the processor 240, and this set (that is, achipset) may be called a processor 240′.

The antenna 201 and the cellular transceiver 210 are used fortransmitting and receiving a cellular radio signal. The cellulartransceiver 210 converts the baseband signal output from the processor240 into the cellular radio signal, and transmits the same from theantenna 201. Furthermore, the cellular transceiver 210 converts thecellular radio signal received by the antenna 201 into the basebandsignal, and outputs the same to the processor 240.

The network interface 220 is connected to the neighboring eNB 200 via anX2 interface and is connected to the MME/S-GW 500 via the S1 interface.Further, the network interface 220 is used for communication with the AP300 via the EPC 20.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240. The processor240 includes the baseband processor that performs modulation anddemodulation, and encoding and decoding of the baseband signal and a CPUthat performs various processes by executing the program stored in thememory 230. The processor 240 implements various processes and variouscommunication protocols described later.

FIG. 4 is a block diagram of the AP 300. As shown in FIG. 4, the AP 300includes an antenna 301, a WLAN transceiver 311, a network interface320, a memory 330, and a processor 340. Furthermore, the memory 330 maybe integrally formed with the processor 340, and this set (that is, achipset) may be called a processor 340′.

The antenna 301 and the WLAN transceiver 311 are used for transmittingand receiving the WLAN radio signal. The WLAN transceiver 311 convertsthe baseband signal output from the processor 340 into the WLAN radiosignal and transmits the same from the antenna 301. Further, the WLANtransceiver 311 converts the WLAN radio signal received by the antenna301 into the baseband signal and outputs the same to the processor 340.

The network interface 320 is connected to the EPC 20 via a router, etc.Further, the network interface 320 is used for communication with theeNB 200 via the EPC 20.

The memory 330 stores a program executed by the processor 340 andinformation used for a process by the processor 340. The processor 340includes the baseband processor that performs modulation anddemodulation, and encoding and decoding of the baseband signal and a CPUthat performs various processes by executing the program stored in thememory 330.

FIG. 5 is a protocol stack diagram of a radio interface in the LTEsystem. As illustrated in FIG. 5, the radio interface protocol isclassified into a layer 1 to a layer 3 of an OSI reference model,wherein the layer 1 is a physical (PHY) layer. The layer 2 includes aMAC (Media Access Control) layer, an RLC (Radio Link Control) layer, anda PDCP (Packet Data Convergence Protocol) layer. The layer 3 includes anRRC (Radio Resource Control) layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. Between the PHY layer of the UE 100 and the PHY layer of theeNB 200, data is transmitted via the physical channel.

The MAC layer performs preferential control of data, and aretransmission process and the like by hybrid ARQ (HARQ). Between theMAC layer of the UE 100 and the MAC layer of the eNB 200, data istransmitted via a transport channel. The MAC layer of the eNB 200includes a scheduler for deciding a transport format (a transport blocksize, a modulation and coding scheme, and the like) of an uplink and adownlink, and an assigned resource block.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data istransmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB 200, a control message (anRRC message) for various types of setting is transmitted. The RRC layercontrols the logical channel, the transport channel, and the physicalchannel in response to establishment, re-establishment, and release of aradio bearer. When there is a connection (RRC connection) between theRRC of the UE 100 and the RRC of the eNB 200, the UE 100 is in aconnected state (RRC connected state), and otherwise, the UE 100 is inan idle state (RRC idle state).

A NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management or mobility management, for example.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency DivisionMultiplexing Access) is applied to a downlink, and SC-FDMA (SingleCarrier Frequency Division Multiple Access) is applied to an uplink,respectively.

As illustrated in FIG. 6, the radio frame is configured by 10 subframesarranged in a time direction, wherein each subframe is configured by twoslots arranged in the time direction. Each subframe has a length of 1 msand each slot has a length of 0.5 ms. Each subframe includes a pluralityof resource blocks (RBs) in a frequency direction, and a plurality ofsymbols in the time direction. The resource block includes a pluralityof subcarriers in the frequency direction.

Among radio resources assigned to the UE 100, a frequency resource canbe designated by a resource block and a time resource can be specifiedby a subframe (or slot).

In the downlink, an interval of several symbols at the head of eachsubframe is a control region mainly used as a physical downlink controlchannel (PDCCH). Furthermore, the remaining interval of each subframe isa region mainly used as a physical downlink shared channel (PDSCH).Furthermore, in the downlink, reference signals such as cell-specificreference signals are dispersed and arranged in each subframe.

In the uplink, both ends, in the frequency direction, of each subframeare control regions mainly used as a physical uplink control channel(PUCCH). Furthermore, the center portion, in the frequency direction, ofeach subframe is a region mainly used as a physical uplink sharedchannel (PUSCH).

(Operation According to First Embodiment)

Subsequently, an operation according to the first embodiment will bedescribed. FIG. 7 is a diagram for illustrating an operation environmentaccording to the first embodiment.

As shown in FIG. 7, the AP 300 (an AP 300-1 to an AP 300-3) is arrangedwithin a coverage of the eNB 200. In the first embodiment, the eNB 200manages a cell over a wide range (large cell). The large cell is ageneral cell in the LTE system, and is called “macro cell”.

Further, it may be possible that within the coverage of the macro cell,a small cell having a narrower coverage than the macro cell is arranged.The small cell is called “pico cell” or “femto cell”. The small cellbelongs to a frequency that is within a cellular frequency band and thatis different from a frequency to which the macro cell belongs. The smallcell is managed by HeNB 400 (pico eNB or femto eNB).

UE 100-1 to UE 100-3 are connected to a cell (macro cell) of the eNB200, and perform cellular communication with the eNB 200. When the eNB200 houses a large number of UEs 100, a load level of the eNB 200increases. That is, an amount of a radio resource (a resource block,etc.) that can be assigned by the eNB 200 to each UE 100 decreases.

The AP 300 is operated by an operator of a cellular communication system(in the present embodiment, the LTE system). Such AP 300 is called“Planned AP”. UE 100-4 is connected to the AP 300-3, and performs WLANcommunication with the AP 300-3. On the other hand, there is no UE 100to be connected to the AP 300-1 and the AP 300-2.

Subsequently, an overview of an operation according to the firstembodiment will be described. In the first embodiment, a load of the eNB200 is dispersed (offloaded) to the AP 300.

Firstly, the UE 100 stores a list on the APs 300 (Planned APs) to whichthe UE 100 is connectable (hereinafter, “AP white list”). The AP whitelist includes identifiers of the APs 300 to which the UE 100 isconnectable. The AP white list may include AP location information on aperipheral location of the AP 300. Alternatively, the AP white list mayfurther include an identifier (cell identifier) of eNB 200. Theidentifier of the AP 300 is SSID (Service Set Identifier) or ESSID(Extended Service Set Identifier), for example.

The UE 100 may autonomously update the AP white list and the eNB 200sets the AP white list to the UE 100, and the both cases may becombined. In a case where the UE 100 autonomously updates the AP whitelist, when the UE 100 is connected to the AP 300 after which there is anotification that the AP 300 is the Planned AP from the AP 300, the APwhite list is updated. On the other hand, in a case where the eNB 200sets the AP white list to the UE 100, the UE 100 receives and stores,from the eNB 200, the AP white list on each AP 300 arranged within thecoverage of the eNB 200. In this case, the AP white list may be managedin a unit of eNB 200 (or a unit of cell), or in a unit of tracking area.

The eNB 200 may determine whether to transmit the AP white list to theUE 100 before transmitting the AP white list to the UE 100. For example,the eNB 200 does not transmit the AP white list to the UE 100 when it isassumed that the UE 100 will be out of coverage of the eNB 200 byestimating that the UE 100 is moving at high speed based on the numberof handovers per a time unit or location information and the like.Alternatively, such determination may be performed by the UE 100.Specifically, the UE 100 storing the AP white list does not use the APwhite list when it is assumed that the UE 100 will be out of coverage ofthe eNB 200 by estimating that the UE 100 is moving at high speed basedon the number of handovers per a time unit or location information andthe like.

The eNB 200 may adjust the number of Aps 300 included in the AP whitelist before transmitting the AP white list to the UE 100. For example,the eNB 200 decreases the number of Aps 300 included in the AP whitelist by limiting geographical range of APs 300 to be included in the APwhite list when the eNB 200 determines that the moving velocity of UE100 is low by estimating the moving velocity of UE 100 based on thenumber of handovers per a time unit or location information and thelike. Alternatively, such adjustment may be performed by the UE 100.Specifically, the UE 100 storing the AP white list decreases the numberof APs 300 to be targeted among APs 300 included in the AP white list,when the UE 100 determines that the moving velocity of UE 100 is low byestimating the moving velocity of UE 100 based on the number ofhandovers per a time unit or location information and the like.

The UE 100 may determine whether to use the AP white list, byconsidering one of a traffic amount and a traffic type exchanged by theUE 100, or radio communication environment of the UE 100. For example,the UE 100 uses the AP white list, when the traffic amount exchanged bythe UE 100 is heavy or when the QoS of traffic exchanged by the UE 100is low. Otherwise, the UE 100 does not use the AP white list.

The eNB 200 may set the AP white list to the UE 100 without including APinformation in the AP white list when the offload is unnecessary.

Secondly, the UE 100 detects the UE 100 having approached the AP 300, onthe basis of the AP white list, when the UE 100 is connected to the eNB200 and the WLAN transceiver 112 is in an OFF state. The UE 100 iscapable of detecting the UE 100 approaching the AP 300, for example, bycomparing the UE location information grasped by the GNSS receiver 130or the UE location information obtained from a network, with the APlocation information. Here, as described above, “detecting approaching”means “recognition of approaching”, and may mean not actuallyapproaching (may mean erroneous detection). Alternatively, in a casewhere cell identifiers are included in the AP white list, the UE 100 maydetect the UE 100 approaching the AP 300 by comparing a cell identifierof connection destination with the cell identifiers included in the APwhite list.

Thirdly, the UE 100 detects the UE 100 having approached the AP 300, andthen, switches the WLAN transceiver 112 to an ON state after which theUE 100 performs a WLAN scanning. Specifically, the UE 100 confirmswhether it is possible to receive a WLAN signal (beacon signal) from theAP 300. The UE 100 may perform a WLAN scanning on the beacon signalincluding the identifier (SSID/ESSID) of the AP 300 that was detected,by the UE 100, being approached, on the basis of the AP white list.

Therefore, the UE 100 that is approaching the AP 300 is capable ofdiscovering the AP 300. As a result, it is possible for the UE 100 to beconnected to the AP 300, and thus, it is possible to efficiently use theAP 300 and disperse (offload) the load of the eNB 200 to the AP 300.

Subsequently, a specific example of an operation according to the firstembodiment will be described. FIG. 8 is sequence diagram of an operationpattern 1 according to the first embodiment. In an initial state of FIG.8, the UE 100 is connected to the eNB 200 and sets so that the WLANtransceiver 112 is in an OFF state. Further, the eNB 200 and the AP 300perform a negotiation for operating in interworking with each other(step S1101).

As shown in FIG. 8, in step S1102, the eNB 200 transmits the AP whitelist to the UE 100. For example, the AP white list is transmitted byusing an RRC message. The UE 100 stores the AP white list received fromthe eNB 200. In a case where the UE 100 autonomously updates the APwhite list, the step S1102 may be unnecessary.

In step S1103, the UE 100 determines whether or not the UE 100approaches the AP 300 on the basis of the AP white list. In this case,description is provided on the assumption that the UE 100 has approachedthe AP 300.

In step S1104, the UE 100 switches the WLAN transceiver 112 to the ONstate, and starts a WLAN scanning.

In step S1105, the UE 100 receives the beacon signal from the AP 300.

In step S1106, the UE 100 discovers the AP 300 on the basis of thebeacon signal received from the AP 300. Further, the UE 100 extracts anidentifier (SSID/ESSID) included in the beacon signal received from theAP 300.

In step S1107, the UE 100 transmits a discovery notification indicatingthat the AP 300 was discovered (AP discovery indication), to the eNB200. The AP discovery indication includes the identifier (SSID/ESSID) ofthe discovered AP 300.

In step S1108, the eNB 200 determines whether or not the UE 100 is madeto be connected to the AP 300 (that is, whether to perform the offload)on the basis of the AP discovery indication received from the UE 100.The eNB 200 may perform such a determination in consideration of theload level of the eNB 200 and an amount or a category of the traffic,for example, that the UE 100 transmits and receives. For example, theeNB 200 determines that the UE 100 is made to be connected to the AP300, when the load level of the eNB 200 is high. Further, the eNB 200determines that the UE 100 is made to be connected to the AP 300, when atraffic amount that the UE 100 transmits and receives is large, or whenQoS of a traffic that the UE 100 transmits and receives is small. Inthis case, description is provided on the assumption that the eNB 200determines that the UE 100 is made to be connected to the AP 300.

In step S1109, the eNB 200 transmits request information requesting aconnection by the UE 100 to the AP 300, to the AP 300.

In step S1110, the AP 300 transmits a response (Ack) to the requestinformation transmitted from the eNB 200, to the eNB 200.

In step S1111, the eNB 200 transmits a connection instruction toinstruct a connection to the AP 300, to the UE 100, in response toreceiving the response (Ack) from the AP 300. The connection instructionmay include information designating a category of the traffic that theUE 100 should transmit to and receive from the AP 300.

The UE 100 connects to the AP 300 when receiving the connectioninstruction from the eNB 200, and starts WLAN communication with the AP300. When the connection instruction includes the informationdesignating the traffic type, the UE 100 transmits and receives thedesignated traffic type by the WLAN communication.

The UE 100 may notify the eNB 200 of the completion of the connectionwhen the connection with the AP 300 is completed. Alternatively, the AP300 may notify the eNB 200 of the connection by the UE 100.

On the other hand, when the connection instruction from the eNB 200 isnot received until a predetermined timer time elapses since the UE 100transmitted the AP discovery indication to the eNB 200, the UE 100 maydetermine a time-out and switch the WLAN transceiver 112 to an OFFstate. Alternatively, when a connection suspension instructioninstructing not to connect to the AP 300 is transmitted from the eNB 200to the UE 100 and the UE 100 receives the connection suspensioninstruction, the WLAN transceiver 112 may be switched to an OFF state.

FIG. 9 is a sequence diagram of an operation pattern 2 according to thefirst embodiment. In this case, a difference from the operation pattern1 will be mainly described.

As shown in FIG. 9, steps S1201 to S1204 are the same as those in theoperation pattern 1. However, in the operation pattern 2, in step S1201,the eNB 200 may grasp whether or not the AP 300 is in an OFF state(sleep state).

After the UE 100 detects the UE 100 approaching the AP 300 (step S1203)and the WLAN transceiver 112 is switched to an ON state (step S1204), instep S1205, the UE 100 transmits a proximity notification indicatingthat the UE 100 approaches the AP 300, to the eNB 200. The proximitynotification includes the identifier (SSID/ESSID) of the AP 300 that wasdetected, by the UE 100, approaching. It is noted that step S1204 may beperformed after step S1205 or after step S1206. An AP discoverynotification (measurement report) may be used instead of the proximitynotification.

In step S1205 a, when the AP 300 corresponding to the identifier(SSID/ESSID) included in the proximity notification from the UE 100 isin an OFF state, the eNB 200 starts up the AP 300. The eNB 200 maytransmit, to the AP 300, a setting request requesting to set to shortena transmission cycle of the beacon signal in a constant period, when theAP 300 is in an ON state.

In step S1206, the eNB 200 transmits, to the UE 100, a scanninginstruction instructing the WLAN scanning. The scanning instructionincludes information on designating a timing, a frequency, etc., atwhich the WLAN scanning should be performed. The timing at which theWLAN scanning should be performed preferably is set to a timing at whichthe AP 300 broadcasts the beacon signal. Such a broadcast timing may beexpressed in an offset on the basis of the timing of the eNB 200. The UE100 performs the WLAN scanning in accordance with the timing, thefrequency, etc., set by the scanning instruction received from the eNB200.

It is noted that the eNB 200 may set again a measurement cycle of thecellular communication to the UE 100 in consideration of the timing atwhich the AP 300 broadcasts the beacon signal. Such a setting preferablyis set to a timing at which the cellular communication is not measuredat the timing of the WLAN scanning.

In step S1207, the UE 100 receives the beacon signal from the AP 300.

In step S1208, the UE 100 discovers the AP 300 on the basis of thebeacon signal received from the AP 300. Further, the UE 100 extracts anidentifier (SSID/ESSID) included in the beacon signal received from theAP 300.

In step S1209, the UE 100 transmits the discovery notification (APdiscovery indication) showing that the AP 300 was discovered, to the eNB200. The AP discovery indication includes the identifier (SSID/ESSID) ofthe discovered AP 300. The AP discovery indication may includemeasurement information (received power, etc.) on the beacon signal fromthe AP 300.

The subsequent operations are the same as those in the operationpattern 1. However, the eNB 200 may request the AP 300 to restore thetransmission cycle of the beacon signal to the original state, when theAP 300 is requested to set to shorten the transmission cycle of thebeacon signal in a constant period and the constant period does notexpire at a time point at which it is notified, by the UE 100, theeffect that the UE 100 is connected to the AP 300.

Second Embodiment

For a second embodiment, a difference from the above-described firstembodiment will be mainly described. A system configuration and anoperation environment according to the second embodiment are the same asthose in the first embodiment. However, the second embodiment differsfrom the first embodiment in that the former is led by the eNB 200.

Firstly, an overview of an operation according to the second embodimentwill be described. In the second embodiment, the eNB 200 transmits, toone or a plurality of UEs 100 connected to the eNB 200, triggerinformation for scanning the AP 300. The eNB 200 may transmit thetrigger information when the load level of the eNB 200 is high (exceedsa threshold).

In an operation pattern 1 according to the second embodiment, thetrigger information is information instructing to switch the WLANtransceiver 112 to an ON state. The eNB 200 transmits the triggerinformation to the selected UE 100. The UE 100 switches the WLANtransceiver 112 to an ON state and performs the WLAN scanning, when theUE 100 receives the trigger information.

In an operation pattern 2 according to the second embodiment, thetrigger information includes the AP location information indicating alocation of the AP 300. The eNB 200 transmits the trigger information tothe selected UE 100. The UE 100 switches the WLAN transceiver 112 to anON state and performs the WLAN scanning, when the UE 100 receives thetrigger information and detects the UE 100 having approached the AP 300on the basis of the AP location information.

In an operation pattern 3 according to the second embodiment, thetrigger information includes condition information indicating acondition under which to perform a scan. The eNB 200 transmits thetrigger information by broadcast. The UE 100 switches the WLANtransceiver 112 to an ON state and performs the WLAN scanning, when theUE 100 receives the trigger information and detects that a conditionunder which to perform the WLAN scanning is satisfied, on the basis ofthe condition information.

In another operation pattern according to the second embodiment, thetrigger information may be an offload preference indicator.Alternatively, network selection parameters may be used in addition tothe trigger information or instead of the trigger information. Otheroperation patterns will be described in the seventh embodiment and theadditional statements.

Subsequently, a specific example of an operation according to the secondembodiment will be described. FIG. 10 is a sequence diagram of theoperation pattern 1 according to the second embodiment. In an initialstate of FIG. 10, the UE 100 (UE 100-1 to UE 100-N) is connected to theeNB 200 and sets so that the WLAN transceiver 112 is in an OFF state.Further, the eNB 200 and the AP 300 perform a negotiation for operatingin interworking with each other (step S2101).

As shown in FIG. 10, in step S2102, the eNB 200 transmits the requestinformation requesting a connection by the UE 100 to the AP 300, to theAP 300.

In step S2103, the AP 300 transmits, to the eNB 200, a response (Ack) tothe request information transmitted from the eNB 200. The eNB 200 storesthe identifier (SSID/ESSID) of the AP 300 from which the response (Ack)is obtained.

In step S2104, the eNB 200 selects the UE 100 to which the triggerinformation is to be transmitted. The eNB 200 may make such adetermination in consideration of an amount or a category of the trafficthat the UE 100 transmits and receives, a radio communicationenvironment of the UE 100, etc. For example, the eNB 200 selects the UE100 as a target to which the trigger information is transmitted, when atraffic amount that the UE 100 transmits and receives is large or QoS ofa traffic that the UE 100 transmits and receives is small.Alternatively, the eNB 200 may estimate a distance between the UE 100and the eNB 200 on the basis of a pathloss or a timing advance, forexample, and select a remote UE 100 as a target to which the triggerinformation is transmitted. Alternatively, the eNB 200 may determinewhether or not the UE 100 is at a cell edge on the basis of radioquality information between the eNB 200 and the UE 100, and select theUE 100 determined to be at the cell edge as a target to which thetrigger information is transmitted.

It is noted that the eNB 200 may inquire each UE 100 of the presence orabsence of a WLAN support, prior to step S2104. Alternatively, the eNB200 may previously grasp whether the UE 100 provides the WLAN support,as Capability information of the UE 100. In this case, the Capabilityinformation notified from the UE 100 to the eNB 200 includes informationon whether the UE 100 provides the WLAN support. The eNB 200 excludes UE100 that does not support the WLAN, from a selection target.

In step S2105, the eNB 200 transmits, as the trigger information,information (WLAN turning on instruction) instructing the selected UE100 to switch the WLAN transceiver 112 to an ON state.

In step S2106, the UE 100 that received the trigger information (WLANturning on instruction) switches the WLAN transceiver 112 to an ONstate, and performs a scanning. It is noted that when the UE 100 thatdoes not support the WLAN receives the trigger information, the triggerinformation may be ignored and the eNB 200 may be notified to thateffect.

In step S2107, the UE 100 discovers the AP 300 on the basis of thebeacon signal received from the AP 300. Further, the UE 100 extracts anidentifier (SSID/ESSID) included in the beacon signal received from theAP 300.

In step S2108, the UE 100 transmits an AP discovery indicationindicating that the AP 300 was discovered, to the eNB 200. The APdiscovery indication includes the identifier (SSID/ESSID) of thediscovered AP 300.

In step S2109, the eNB 200 determines whether or not the UE 100 is madeto be connected to the AP 300 (that is, whether or not to perform anoffload), on the basis of the AP discovery indication received from theUE 100. The determination method is the same as that in the firstembodiment. However, in the second embodiment, the eNB 200 determinesthat the UE 100 that discovers the AP 300 from which the response (Ack)is not obtained should not be connected to the AP 300.

In step S2110, the eNB 200 transmits a connection instructioninstructing a connection to the AP 300, to the UE 100 that is determinedto be connected to the AP 300. The connection instruction may includeinformation designating a category of the traffic that the UE 100 shouldtransmit to and receive from the AP 300.

The UE 100 connects to the AP 300 when receiving the connectioninstruction from the eNB 200, and starts WLAN communication with the AP300. Further, when connection instruction includes informationdesignating the traffic type, the designated traffic type is transmittedand received by the WLAN communication.

In step S2111, the eNB 200 determines whether or not the load leveldispersed (offloaded) to the AP 300 exceeds a threshold (that is,whether or not the load level of the eNB 200 decreases to a targetvalue). When the offloaded load level is less than the threshold, theprocess returns to step S2104.

FIG. 11 is a sequence diagram of the operation pattern 2 according tothe second embodiment. In this case, a difference from the operationpattern 1 will be mainly described.

As shown in FIG. 11, steps S2201 to S2204 are the same as those in theoperation pattern 1.

In step S2205, the eNB 200 transmits, as the trigger information,information instructing the selected UE 100 to switch the WLANtransceiver 112 to an ON state (WLAN turning on instruction). Thetrigger information includes AP location information.

In steps S2206 and S2207, the UE 100 that received the triggerinformation (WLAN turning on instruction) determines whether or not theUE 100 approaches the AP 300 on the basis of the AP location informationand the UE location information included in the WLAN turning oninstruction. Such a determination method is the same as that in thefirst embodiment.

The UE 100 that determined to approach the AP 300 switches the WLANtransceiver 112 to an ON state and performs the WLAN scanning, in stepS2208. The subsequent operations (steps S2209 to S2213) are the same asthose in the operation pattern 1.

FIG. 12 is the sequence diagram of an operation pattern 3 according tothe second embodiment. In this case, a difference from the operationpattern 1 will be mainly described.

As shown in FIG. 12, steps S2301 to S2303 are the same as those in theoperation pattern 1.

In step S2304, the eNB 200 decides a condition under which to performthe WLAN scanning (scanning execution condition). Examples of thescanning execution condition may include a condition that the WLAN issupported. The scanning execution condition may be defined according toan operator policy.

In step S2305, the eNB 200 transmits, to each UE 100 connecting to theeNB 200, the trigger information including the scanning executioncondition by the broadcast. That is, such trigger information may beregarded as conditional WLAN turning on instruction.

The UE 100 that received the trigger information determines whether ornot the scanning execution condition is satisfied, in step S2306. The UE100 that determined that the scanning execution condition is satisfiedswitches the WLAN transceiver 112 to an ON state and performs the WLANscanning, in step S2307. The subsequent operations are the same as thosein the operation pattern 1.

In the second embodiment, the UE 100 may determine whether to use theinformation received from the eNB 200. For example, the UE 100 does notuse the information received from the eNB 200, when it is assumed thatthe UE 100 will be out of the coverage of the eNB 200 by estimating thatthe UE 100 is moving at high speed based on the number of handovers pera time unit or location information and the like.

Alternatively, the UE 100 may determine whether to use the informationreceived from the eNB 200, on the basis of one of a traffic amount and atraffic type exchanged by the UE 100, or radio communication environmentof the UE 100. For example, the UE 100 uses the information receivedfrom the eNB 200, when the traffic amount exchanged by the UE 100 isheavy or when the QoS of traffic exchanged by the UE 100 is low.Otherwise, the UE 100 does not use the AP white list.

Third Embodiment

A third embodiment will be described on the basis mainly of a differencefrom the above-described first embodiment and second embodiment.

The AP 300 according to the third embodiment is configured to be capableof transmitting a discovery signal (beacon signal) within a cellularfrequency band. FIG. 13 is a block diagram of the AP 300 according tothe third embodiment. As shown in FIG. 13, the AP 300 includes acellular transceiver 312 in addition to the WLAN transceiver 311. Otherconfigurations are the same as those in the first embodiment.

Further, in the third embodiment, it is possible to offload not only tothe AP 300 but also to the small cell. In the third embodiment, HeNB 400(see FIG. 7) that manages a small cell is configured to be capable oftransmitting the discovery signal at a frequency (first frequency) towhich the macro cell belongs. The discovery signal transmitted by theHeNB 400 (small cell) may be one type of a cell-specific referencesignal (CRS), and may be a signal transmitted in a higher density and alonger cycle than a normal CRS. FIG. 14 is a block diagram of the HeNB400 according to the third embodiment. As shown in FIG. 14, the HeNB 400includes, in addition to a cellular transceiver 411 for a small cellband (second frequency), a cellular transceiver 412 for a macro cellband (first frequency). Other configurations are the same as those inthe eNB 200.

Hereinafter, the AP 300 and the eNB 400 are called “specific apparatus”,where appropriate. In the third embodiment, as shown in FIG. 15, thespecific apparatus broadcasts the discovery signal for informing of thepresence of the specific apparatus within a cellular frequency band andin a specific period. The UE 100 connecting to the eNB 200 scans thediscovery signal, by the cellular transceiver 111, within a cellularfrequency band and in a specific period. In the third embodiment, thespecific period is configured in a unit of subframe; however, thespecific period may be configured in a unit of another time (such as aslot and a symbol).

That is, while the AP 300 performs WLAN communication in a WLANfrequency band different from the cellular frequency band, the AP 300broadcasts the discovery signal (beacon signal) within the cellularfrequency band. Further, while the HeNB 400 performs cellularcommunication within a small cell band, the HeNB 400 broadcasts thediscovery signal within a macro cell band.

As a result, the UE 100 connecting to the eNB 200 (macro cell) iscapable of being connected to the eNB 200 and receiving the discoverysignal from the specific apparatus (the AP 300 and the HeNB 400), andthus, it is possible to easily discover the specific apparatus duringbeing connected to the eNB 200. As a result, it is possible to connectthe UE 100 to the specific apparatus. It is noted that the specificapparatus may suspend the broadcast of the discovery signal when theload level of the specific apparatus is high.

Information (such as subframe number) on the specific subframe may bepreviously stored in the UE 100, and may be notified by the eNB 200 tothe UE 100. When the specific subframe is notified by the eNB 200 to theUE 100, the eNB 200 may cause the UE 100 to recognize the specificsubframe as a subframe for MBMS (Multimedia Broadcast MulticastService).

The eNB 200 and the specific apparatus preferably are synchronized;however, when asynchronous to each other, the specific apparatus needsto be synchronized with the eNB 200. The specific apparatus includes afunction of communicating in the macro cell frequency band, and thus,when the specific apparatus accesses, as the UE 100, the eNB 200, it ispossible to detect a downlink subframe timing of the eNB 200. In thiscase, the specific apparatus may detect the downlink subframe timing ofthe eNB 200 on the basis of the timing advance assigned from the eNB200.

Further, in order for the UE 100 to easily receive the discovery signal,the eNB 200 preferably suspends the transmission by the eNB 200 and/ortransmission by the UE 100 connecting to the eNB 100 in a specificsubframe.

Subsequently, a specific example of an operation according to the thirdembodiment will be described in which the specific apparatus is the AP300. FIG. 16 is a sequence diagram of an operation pattern 1 accordingto the third embodiment. In an initial state of FIG. 16, the UE 100 isconnected to the eNB 200 and sets so that the WLAN transceiver 112 is inan OFF state. Further, the eNB 200 and the AP 300 perform a negotiationfor operating in interworking with each other (step S3101).

As shown in FIG. 16, in step S3102, the AP 300 broadcasts the discoverysignal within a cellular frequency band and in a specific subframe. Thediscovery signal includes the identifier (SSID/ESSID) of the AP 300. TheUE 100 connecting to the eNB 200 scans the discovery signal within acellular frequency band and in a specific subframe.

In step S3103, the UE 100 detects, by the scan, the discovery signal(that is, discovers the AP 300) from the AP 300. Further, the UE 100extracts the identifier (SSID/ESSID) included in the detected discoverysignal.

In step S3104, the UE 100 transmits an AP discovery indicationindicating that the AP 300 was discovered, to the eNB 200. The APdiscovery indication includes the identifier (SSID/ESSID) of thediscovered AP 300.

In step S3105, the eNB 200 determines whether or not the UE 100 is madeto be connected to the AP 300 (that is, whether or not performs theoffload) on the basis of the AP discovery indication received from theUE 100. Such a determination method is the same as that in the firstembodiment. In this case, description is provided on the assumption thatthe eNB 200 determines that the UE 100 is made to be connected to the AP300.

In step S3106, the eNB 200 transmits the connection instructioninstructing the connection to the AP 300, to the UE 100. The connectioninstruction may include information designating a category of thetraffic that the UE 100 should transmit to and receive from the AP 300.It is noted that at this time point, the WLAN transceiver 112 of the UE100 is in an OFF state, and therefore, it is possible to regard theconnection instruction as a WLAN scanning instruction.

In step S3107, in response to receiving connection instruction from theeNB 200, the UE 100 switches the WLAN transceiver 112 to an ON state,and starts the WLAN scanning in a WLAN frequency band.

In step S3108, when the AP 300 is not discovered by the scanning in aWLAN frequency band, the UE 100 determines that the WLAN transceiver 311of the AP 300 is in an OFF state (sleep state), and transmits a WLAN onrequest to the eNB 200 (step S3109). Then, in step S3110, in response tothe WLAN on request from the UE 100, the eNB 200 transmits a start-upinstruction to the AP 300. As a result, the WLAN transceiver 311 of theAP 300 is switched to an ON state, a transmission of the beacon signalfrom the WLAN transceiver 311 is started (step S3111). Further, in stepS3113, the AP 300 transmits, to the eNB 200, an notification to theeffect that the start-up.

In step S3112, as a result of the scanning in the WLAN frequency band,the UE 100 detects the beacon signal (that is, discovers the AP 300)from the AP 300.

In step S3114, the UE 100 is connected to the AP 300, and starts WLANcommunication with the AP 300. When the connection instruction includesthe information designating the traffic type, the designated traffictype is transmitted and received by the WLAN communication.

The UE 100 may notify the eNB 200 of the completion of the connectionwhen the connection with the AP 300 is completed. Alternatively, the AP300 may notify the eNB 200 of the connection by the UE 100.

FIG. 17 is a sequence diagram of an operation pattern 2 according to thethird embodiment. In this case, a difference from the operation pattern1 will be mainly described.

In the above-described operation pattern 1, whether or not the UE 100 ismade to be connected to the AP 300 is determined before the UE 100discovers the AP 300 in the WLAN frequency band. On the other hand, inthe operation pattern 2, as shown in FIG. 17, such a determination (stepS3212) is performed after the UE 100 discovers the AP 300 in the WLANfrequency band (step S3209).

Specifically, in step S3211, the UE 100 transmits, to the eNB 200, theAP discovery indication indicating that the AP 300 was discovered in theWLAN frequency band. The AP discovery indication includes the identifier(SSID/ESSID) of the discovered AP 300.

In step S3212, the eNB 200 determines whether or not the UE 100 is madeto be connected to the AP 300 (that is, whether or not performs theoffload) on the basis of the AP discovery indication received from theUE 100. In this case, description is provided on the assumption that theeNB 200 determines that the UE 100 is made to be connected to the AP300.

In step S3213, the eNB 200 transmits, to the UE 100, the connectioninstruction instructing the connection to the AP 300. The connectioninstruction may include information designating a category of thetraffic that the UE 100 should transmit to and receive from the AP 300.

In step S3214, in response to the connection instruction from the eNB200, the UE 100 is connected to the AP 300, and starts WLANcommunication with the AP 300. Further, when connection instructionincludes information designating the traffic type, the designatedtraffic type is transmitted and received by the WLAN communication.

Subsequently, a specific example of an operation according to the thirdembodiment will be described in which the specific apparatus is the HeNB400 (small cell). When the specific apparatus is the HeNB 400, the sameprocedure as that in the operation pattern 1 may be applied, and thesame procedure as that in the operation pattern 2 may be applied.

However, when a plurality of HeNBs 400 are arranged within a coverage ofthe HeNB 200, the transmission timing of the discovery signal preferablyis set as follows: FIG. 18 shows a state where a plurality of HeNBs 400transmit the discovery signal all at once in the same subframe. On theother hand, FIG. 19 shows a state where a plurality of HeNBs 400 aregrouped in a specific group unit and the discovery signal is transmittedin a subframe different depending on each group.

When a plurality of HeNBs 400 are arranged within the coverage of theeNB 200, each HeNB 400 transmits the discovery signal in the frequencyband (macro cell frequency band) of the eNB 200. However, the frequencyband actually used by the HeNB 400 for communication is not the same,and the UE 100 does not support all the frequency bands. Therefore, evenwhen the UE 100 detects the discovery signal from the HeNB 400 in themacro cell frequency band, if the frequency band of the HeNB 400 is notsupported, then it is not possible to connect to the eNB 400.

In this case, the HeNBs 400 are grouped into each frequency band, andthe discovery signal is to be transmitted in the subframe differentdepending on each group. Further, the UE 100 scans the discovery signalonly in the subframe corresponding to the frequency band supported bythe UE 100. In this way, the UE 100 is capable of discovering only theconnectable HeNB 400.

It is noted that in the third embodiment, the AP 300 and the HeNB 400are employed as the specific apparatus; however, the specific apparatusmay be UE that supports an inter-terminal radio communication. Theinter-terminal radio communication is called D2D (Device to Device)communication. In the D2D communication, a plurality of UEs directlyperform communication without passing through the EPC 20. The UE thatperforms D2D communication within a cellular frequency band is capableof being positioned equally to the HeNB 400. On the other hand, the UEthat performs D2D communication outside the cellular frequency band iscapable of being positioned equally to the AP 300. Further, when aplurality of specific apparatus are included within the coverage of theeNB 200, the specific apparatus may be collected into each group and thediscovery signal may be transmitted in a subframe different depending oneach group.

Alternatively, the specific apparatus may be a cellular base stationthat performs communications in an unlicensed band.

Fourth Embodiment

A fourth embodiment will be described on the basis mainly of adifference from the above-described first embodiment to thirdembodiment. A system configuration and an operation environmentaccording to the fourth embodiment are the same as those in the thirdembodiment.

In the above-described third embodiment, the AP 300 transmits the beaconsignal as the discovery signal within the cellular frequency band. Onthe other hand, in the fourth embodiment, the AP 300 transmits a normalcellular reference signal (for example, CRS) within the cellularfrequency band rather than transmitting the beacon signal within thecellular frequency band.

In the fourth embodiment, a cell identifier for identifying the AP 300is assigned to the AP 300. That is, the AP 300 belongs to a WLAN system;the AP 300 is assigned the cell identifier used for the cellularcommunication system (LTE system). The eNB 200 stores the cellidentifier assigned to the AP 300.

FIG. 20 is a sequence diagram according to the fourth embodiment. In aninitial state of FIG. 20, the UE 100 is connected to the eNB 200 andsets so that the WLAN transceiver 112 is in an OFF state. Further, theeNB 200 and the AP 300 perform a negotiation for operating ininterworking with each other (step S4101).

As shown in FIG. 20, in step S4102, the AP 300 broadcasts the cellularreference signal within the cellular frequency band. The cellularreference signal transmitted by the AP 300 includes the cell identifierassigned to the AP 300.

The UE 100 connecting to the eNB 200 receives the cellular referencesignal broadcast from the AP 300 within the cellular frequency band. Inthis case, when seen from the UE 100, it is not possible to know thatthe transmission source of the cellular reference signal is the AP 300,and thus, measurement on the cellular reference signal (for example,measurement on a received power) is performed according to a normaloperation, and measurement information indicating a measurement resultis reported to the eNB 200 (step S4104). The measurement informationincludes a cell identifier of a cell to be measured.

In step S4105, on the basis of the measurement information reported fromUE 100, the eNB 200 determines whether or not the UE 100 received thecellular reference signal from the AP 300. Once the eNB 200 confirmsthat the cell identifier included in the measurement information matchesthe cell identifier assigned to the AP 300, for example, the eNB 200determines that the UE 100 received the cellular reference signal fromthe AP 300.

In step S4106, the eNB 200 determines whether or not the UE 100 is madeto be connected to the AP 300 (that is, whether or not performs theoffload). Such a determination method is the same as that in the firstembodiment. The subsequent operations are the same as those in theoperation pattern 1 according to the third embodiment.

Instead of AP 300, a cellular base station that performs communicationsin an unlicensed band may be used in the fourth embodiment.

Fifth Embodiment

A fifth embodiment will be described on the basis mainly of a differencefrom the above-described first embodiment to fourth embodiment. A systemconfiguration and an operation environment according to the fifthembodiment are the same as those in the third embodiment.

In the fifth embodiment, the AP 300 detects the UE 100 having approachedthe AP 300 by detecting a cellular uplink signal transmitted from the UE100 connecting to the eNB 200. The AP 300 transmits, to the eNB 200, anotification indicating that the UE 100 approaches the AP 300 on thebasis of the detection of the cellular uplink signal. The eNB 200transmits, to the UE 100, information for scanning the AP 300 on thebasis of the notification from the AP 300.

In operation pattern 1 and 2 according to the fifth embodiment, the AP300 acquires, from the eNB 200, signal information on the cellularuplink signal transmitted by the UE 100, and on the basis of the signalinformation, the AP 300 estimates a pathloss between the UE 100 and theAP 300. The AP 300 determines that the UE 100 approaches the AP 300 whenthe pathloss is less than a threshold.

In an operation pattern 3 according to the fifth embodiment, the AP 300determines whether or not the UE 100 approaches the AP 300 on the basisof a distance between the AP 300 and the eNB 200 and a received power ofthe cellular uplink signal.

FIG. 21 is a sequence diagram of the operation pattern 1 according tothe fifth embodiment. In an initial state of FIG. 21, the UE 100 isconnected to the eNB 200 and sets so that the WLAN transceiver 112 is inan OFF state. Further, the eNB 200 and the AP 300 perform a negotiationfor operating in interworking with each other (step S5101).

As shown in FIG. 21, in step S5102, the AP 300 transmits the beaconsignal.

In step S5103, the UE 100 transmits the cellular uplink signal to theeNB 200. The cellular uplink signal may be an uplink reference signal(SRS: Sounding Reference Signal), for example.

In step S5104, the AP 300 receives the cellular uplink signal from theUE 100, and detects the presence of the UE 100. Further, the AP 300measures the received power of the cellular uplink signal from the UE100, and specifies a resource element corresponding to the cellularuplink signal.

In step S5105, the AP 300 transmits the information on the specifiedresource element to the eNB 200. The AP 300 may transmit alsoinformation on the measured uplink received power to the eNB 200.

In step S5106, on the basis of the resource element information receivedfrom the AP 300, the eNB 200 specifies the UE 100 to which that resourceelement is assigned. It is noted that in the fifth embodiment, it isassumed that the eNB 200 stores information on an assignment history.

In step S5107, the eNB 200 specifies SRS setting information and anuplink transmission power of the specified UE 100.

In step S5108, the eNB 200 transmits, to the AP 300, the specified SRSsetting information and information on uplink transmission power.

In step S5109, the AP 300 estimates the pathloss between the UE 100 andthe AP 300 on the basis of the SRS setting information and the uplinktransmission power received from the eNB 200. It is possible to obtainthe pathloss by subtracting “the received power of the AP 300 (receivedpower measured in step S5104) from “the transmission power of the UE 100(the transmission power obtained in step S5108)”.

In step S5110, the AP 300 confirms whether or not the pathloss is lessthan a threshold by comparing the estimated pathloss with the threshold.In this case, description is provided on the assumption that thepathloss is less than a threshold.

In step S5111, the AP 300 transmits, to the eNB 200, a notificationindicating that the UE 100 approaches the AP 300.

In step S5112, the eNB 200 determines whether or not the UE 100 is madeto be connected to the AP 300. Such a determination method is the sameas that in the first embodiment. In this case, description is providedon the assumption that it is determined that the UE 100 is made to beconnected to the AP 300.

In step S5113, the eNB 200 transmits, to the UE 100, a connectioninstruction (scanning instruction) instructing a connection to the AP300. The connection instruction includes the identifier (SSID/ESSID) ofthe AP 300.

In step S5114, in response to the receipt of the connection instruction,the UE 100 switches the WLAN transceiver 112 to an ON states, andperforms a scanning.

In step S5115, the UE 100 discovers the AP 300 by the scan.

In step S5116, the UE 100 is connected to the AP 300.

FIG. 22 is a sequence diagram of the operation pattern 2 according tothe fifth embodiment. In this case, a difference from the operationpattern 1 will be mainly described. The operation pattern 2 differs fromthe operation pattern 1 in the approach detection method in the AP 300.

As shown in FIG. 22, steps S5201 to S5203 are the same as those in theoperation pattern 1.

In step S5204, the AP 300 transmits, to the eNB 200, a notificationindicating that the cellular uplink signal from the UE 100 is received.

In step S5205, the eNB 200 determines whether or not the UE 100 is madeto be connected to the AP 300. In this case, the eNB 200 determinesroughly, e.g., determines only the need of the offload. In this case,description is provided on the assumption that the eNB 200 determinesthat the UE 100 is made to be connected to the AP 300.

In step S5206, the eNB 200 transmits, to the AP 300, information (suchas a transmission power, a transmission timing, and a preamble) on aphysical random access channel (PRACH) assigned to the UE 100.

In step S5207, the eNB 200 instructs the UE 100 to transmit the preamble(preamble notified to the AP 300 in step S5206) on the PRACH.

In step S5208, the UE 100 transmits the preamble on the PRACH inaccordance with the instruction from the eNB 200.

In step S5209, the AP 300 detects the preamble from the UE 100 on thebasis of the information from the eNB 200, and measures the receivedpower.

In step S5210, the AP 300 estimates the pathloss between the UE 100 andthe AP 300 on the basis of the detected preamble. It is possible toobtain the pathloss by subtracting “the received power of the AP 300(received power measured in step S5209) from “the transmission power ofthe UE 100 (the transmission power obtained in step S5206)”.

The subsequent operations are the same as those in the operation pattern1.

Subsequently, an operation pattern 3 according to the fifth embodimentwill be described. In the operation pattern 3, after detecting thecellular uplink signal from the UE 100, the AP 300 determines whether ornot the UE 100 approaches the AP 300 without acquiring the informationfrom the eNB 200. Specifically, the AP 300 confirms that the AP 300 isarranged far from the eNB 200, and then, the AP 300 determines that theUE 100 approaches the AP 300 when the received power of the cellularuplink signal from the UE 100 is high.

Instead of AP 300, a cellular base station that performs communicationsin an unlicensed band may be used in the fifth embodiment.

Sixth Embodiment

A sixth embodiment will be described on the basis mainly of a differencefrom the above-described first embodiment to fifth embodiment. A systemconfiguration and an operation environment according to the fifthembodiment are the same as those in the first embodiment.

In the above-described first embodiment to fifth embodiment, the UE 100is made to be connected to the AP 300 to the utmost. On the other hand,in the fifth embodiment, under a specific circumstance, the UE 100 isnot made to be connected to the AP 300 to the most. Specifically, asshown in FIG. 7, the coverage of the AP 300 is narrow, so that the UE100 that moves at high speed quickly passes through the coverage of theAP 300. Therefore, it is efficient for the UE 100 that moves at highspeed not to perform the WLAN scanning.

Therefore, in the sixth embodiment, the UE 100 connecting to the eNB 200derives a moving velocity of the UE 100, and when the moving velocityexceeds a threshold, the UE 100 suspends the WLAN scanning even when theWLAN transceiver 112 is in an ON state.

FIG. 23 is a sequence diagram according to the sixth embodiment. In aninitial state of FIG. 23, the UE 100 is connected to the eNB 200 andsets so that the WLAN transceiver 112 is in an OFF state.

In step S6101, the UE 100 switches the WLAN transceiver 112 to an ONstate, and starts the WLAN scanning.

In step S6102, the UE 100 derives (calculates) the moving velocity ofthe UE 100. It is possible to derive the moving velocity of the UE 100from UE location information obtained from GNSS, for example. Then, theUE 100 determines whether or not the moving velocity of the UE 100exceeds a threshold. In this case, description is provided on theassumption that the UE 100 determines that the moving velocity of the UE100 exceeds a threshold.

In step S6103, the UE 100 suspends the WLAN scanning.

In step S6104, the UE 100 derives (calculates) the moving velocity ofthe UE 100. Then, the UE 100 determines whether or not the movingvelocity of the UE 100 exceeds a threshold. In this case, description isprovided on the assumption that the UE 100 determines that the movingvelocity of the UE 100 is equal to or less than a threshold. In thiscase, the UE 100 resumes the WLAN scanning.

In step S6105, the UE 100 receives the beacon signal from the AP 300.

In step S6106, the UE 100 detects, by the scan, the beacon signal fromthe AP 300 (that is, discovers the AP 300).

It is noted that in the sixth embodiment, the moving velocity of the UE100 serves as the determination criteria to restrict the connection tothe AP 300; however, another determination criteria may be used. Forexample, a traffic type is used as the determination criteria, and whenthe traffic type that the UE 100 transmits and receives is a specifictraffic type (for example, a traffic having high QoS), the connectionrestriction to the AP 300 may be performed. In this case, it is possibleto prevent interruption of the communication by switching the connectionto the AP 300.

Seventh Embodiment

A seventh embodiment will be described on the basis mainly of adifference from the above-described first embodiment to sixthembodiment. A system configuration and an operation environmentaccording to the seventh embodiment are the same as those in the firstembodiment.

In the seventh embodiment, similarly to the sixth embodiment, aconnection restriction to the AP 300 is performed under a specificcircumstance. However, in the seventh embodiment, the connectionrestriction to the AP 300 is performed with being led by the eNB 200.

The eNB 200 according to the seventh embodiment transmits, to the UE 100connecting to the eNB 200, control information controlling whether theUE 100 performs the WLAN scanning.

In an operation pattern 1 according to the seventh embodiment, the eNB200 transmits the control information instructing to perform thescanning when a condition under which to perform the scanning issatisfied, and transmits the control information instructing to suspendthe scanning when the condition is not satisfied.

In an operation pattern 2 according to the seventh embodiment, the eNB200 includes condition information indicating a condition under which toperform the scanning or a condition under which to suspend the scan, inthe control information. In this case, the UE 100 determines whether ornot to suspend the scanning on the basis of the condition information.

FIG. 24 is a sequence diagram of the operation pattern 1 according tothe seventh embodiment. In an initial state of FIG. 24, the UE 100 isconnected to the eNB 200 and sets so that the WLAN transceiver 112 is inan OFF state.

As shown in FIG. 24, in step S7101, the UE 100 switches the WLANtransceiver 112 to an ON state, and starts the WLAN scanning.

In step S7102, the eNB 200 derives (calculates) the moving velocity ofthe UE 100. As the moving velocity of the UE 100, UE moving velocityinformation (number of times of handovers per unit time) managed by theEPC 20, for example, may be used. Then, the eNB 200 determines whetheror not the moving velocity of the UE 100 exceeds a threshold. In thiscase, description is provided on the assumption that the eNB 200determines that the moving velocity of the UE 100 exceeds a threshold.

In step S7103, the eNB 200 transmits the control information instructingto suspend the scan, to the UE 100.

In step S7104, the UE 100 suspends the WLAN scanning in accordance withthe control information from the eNB 200.

In step S7105, the eNB 200 derives (calculates) the moving velocity ofthe UE 100. Then, the eNB 200 determines whether or not the movingvelocity of the UE 100 exceeds a threshold. In this case, description isprovided on the assumption that the eNB 200 determines that the movingvelocity of the UE 100 is equal to or less than a threshold.

In step S7106, the eNB 200 transmits, to the UE 100, the controlinformation instructing to perform the scan. The UE 100 resumes the WLANscanning in accordance with the control information from the eNB 200.

In step S7107, the UE 100 receives the beacon signal from the AP 300.

In step S7108, the UE 100 detects, by the scan, the beacon signal (thatis, discovers the AP 300) from the AP 300.

It is noted that in the operation pattern 1, the moving velocity of theUE 100 serves as the determination criteria to restrict the connectionto the AP 300; however, another determination criteria may be used. Forexample, a traffic type is used as the determination criteria, and whenthe UE 100 starts transmitting and receiving a specific traffic type(for example, a traffic having high QoS), the connection restriction tothe AP 300 may be performed. Alternatively, a load level of the eNB 200is used as the determination criteria, and when the load level of theeNB 200 is low, the connection restriction to the AP 300 may beperformed. Alternatively, radio quality between the UE 100 and the eNB200 is used as the determination criteria, and when the radio quality ishigh, the connection restriction to the AP 300 may be performed.

FIG. 25 is a sequence diagram of the operation pattern 2 according tothe seventh embodiment. In this case, a difference from the operationpattern 1 will be mainly described.

In step S7201, the eNB 200 transmits, to the UE 100, control informationincluding condition information indicating a condition under which toperform the scanning or a condition under which to suspend the scan.Examples of the determination criteria designated by the conditioninformation include a UE moving velocity, the traffic type, and radioquality, as described above.

In step S7202, the UE 100 determines whether or not a conditionindicated by the condition information is satisfied. In this case,description is provided on the assumption that a condition under whichto perform a scanning is not satisfied (or a condition under which tosuspend a scanning is satisfied).

In step S7203, the UE 100 suspends the WLAN scanning.

In step S7204, the UE 100 determines whether or not a conditionindicated by the condition information is satisfied. In this case,description is provided on the assumption that a condition under whichto perform a scanning is satisfied (or a condition under which tosuspend a scanning is not satisfied).

In step S7205, the UE 100 switches the WLAN transceiver 112 to an ONstate, and starts the WLAN scanning.

In step S7206, the UE 100 receives the beacon signal from the AP 300.

In step S7207, the UE 100 detects, by the scan, the beacon signal (thatis, discovers the AP 300) from the AP 300.

Eighth Embodiment

An eighth embodiment will be described on the basis mainly of adifference from the above-described first embodiment to seventhembodiment. A system configuration and an operation environmentaccording to the eighth embodiment are the same as those in the firstembodiment.

In the eighth embodiment, the connection target of the UE 100 isswitched from the AP 300 to the eNB 200. In the eighth embodiment, theUE 100 transmits, to the eNB 200, notification information indicating aswitch from the AP 300 to the eNB 200, when switching the connectiontarget from the AP 300 to the eNB 200. The notification informationincludes an identifier (SSID/ESSID) for identifying the AP 300 and/or anidentifier for identifying the UE 100. The eNB 200 transmits, to the AP300, request information requesting to transfer transmission dataaddressed to the UE 100 to the eNB 200, on the basis of the notificationinformation.

FIG. 26 is a sequence diagram of an operation pattern 1 according to theeighth embodiment. In the operation pattern 1, under a circumstancewhere it is estimated that the UE 100 connecting to the AP 300 movesoutside the coverage of the AP 300, the connection target of the UE 100is switched from the AP 300 to the eNB 200. It is noted that in aninitial state of FIG. 26, the UE 100 is connected to the AP 300 (stepS8101). Further, the eNB 200 and the AP 300 perform a negotiation foroperating in interworking with each other (step S8102).

As shown in FIG. 26, in step S8103, the UE 100 derives (calculates) themoving velocity of the UE 100. It is possible to derive the movingvelocity of the UE 100 from UE location information obtained from GNSS,for example. Then, the UE 100 determines whether or not the movingvelocity of the UE 100 exceeds a threshold. In this case, description isprovided on the assumption that the UE 100 determines that the movingvelocity of the UE 100 is equal to or less than a threshold.

In step S8104, the UE 100 will not switch from the AP 300 to the eNB200.

In step S8105, the UE 100 derives (calculates) the moving velocity ofthe UE 100. Then, the UE 100 determines whether or not the movingvelocity of the UE 100 exceeds a threshold. In this case, description isprovided on the assumption that the UE 100 determines that the movingvelocity of the UE 100 exceeds a threshold.

In step S8106, it is decided to switch the AP 300 to the eNB 200.

In steps S8107 to S8109, the UE 100 performs a random access procedureand an RRC connection establishment procedure, with the eNB 200. In theRRC connection establishment procedure, the UE 100 transmits, to the eNB200, notification information (Out-bound info.) indicating a switch fromthe AP 300 to the eNB 200.

In step S8110, the eNB 200 transmits, to the AP 300, request informationrequesting to transfer transmission data addressed to the UE 100 to theeNB 200, on the basis of the notification information received from theUE 100.

In step S8111, the AP 300 transfers, to the eNB 200, the transmissiondata addressed to the UE 100 in response to the request informationreceived from the eNB 200. The eNB 200 transmits, to the UE 100, thetransmission data received from the AP 300. As a result, it is possibleto seamlessly switch from the AP 300 to eNB 200.

It is noted that in the operation pattern 1, the moving velocity of theUE 100 serves as the determination criteria, and the switchdetermination from the AP 300 to the eNB 200 is performed; however,another determination criteria may be used. For example, a receivedpower (RSSI) of the WLAN signal received by the UE 100 from the AP 300is used as the determination criteria, and when the RSSI falls below athreshold, a switch from the AP 300 to the eNB 200 may be decided.

FIG. 27 is a sequence diagram of an operation pattern 2 according to theeighth embodiment. In the operation pattern 2, under a circumstancewhere the load level of the AP 300 is high, for example, the connectiontarget of the UE 100 is switched from the AP 300 to the eNB 200. In thiscase, a difference from the operation pattern 1 will be mainlydescribed.

In step S8202, the AP 300 determines whether or not to switch theconnection target of the UE 100 from the AP 300 to the eNB 200, on thebasis of the load level of the AP 300. The AP 300 determines to switchthe connection target of the UE 100 from the AP 300 to the eNB 200, whenthe load level of the AP 300 exceeds a threshold, for example. In thiscase, description is provided on the assumption that the AP 300determines that a connection target of the UE 100 is switched from theAP 300 to the eNB 200.

In step S8203, the AP 300 transmits, to the UE 100, a switch instructionto switch from the AP 300 to the eNB 200. The subsequent processes arethe same as those in the operation pattern 1.

It is noted that in the operation pattern 2, the load level of the AP300 served as the determination criteria, and the switch determinationfrom the AP 300 to the eNB 200 is performed; however, anotherdetermination criteria may be used. For example, the moving velocity ofthe UE 100 may be used as the determination criteria.

Instead of AP 300, a cellular base station that performs communicationsin an unlicensed band may be used in the eighth embodiment.

Ninth Embodiment

A ninth embodiment will be described on the basis mainly of a differencefrom the above-described first embodiment to eighth embodiment. A systemconfiguration and an operation environment according to the ninthembodiment are the same as those in the first embodiment.

In the ninth embodiment, similarly to the eighth embodiment, theconnection target of the UE 100 is switched from the AP 300 to the eNB200. In the ninth embodiment, the AP 300 transmits, to the eNB 200,request information requesting to switch to the eNB 200, when theconnection target of the UE 100 is switched from the AP 300 to the eNB200. Then, the AP 300 transmits, to the UE 100, instruction informationinstructing to switch to the eNB 200, when a response to the requestinformation is received from the eNB 200.

FIG. 28 is a sequence diagram according to the ninth embodiment. In aninitial state of FIG. 28, the UE 100 is connected to the AP 300.Further, the eNB 200 and the AP 300 perform a negotiation for operatingin interworking with each other (step S9101). In this case, the AP 300confirms whether the AP 300 is arranged within the coverage of the eNB200.

As shown in FIG. 28, in step S9102, the AP 300 determines whether or notto switch the connection target of the UE 100 from the AP 300 to the eNB200, on the basis of the load level of the AP 300.

In this case, the AP 300 is arranged within the coverage of the eNB 200,and the UE 100 connecting to the AP 300 is ensured that radio qualitywith the eNB 200 is equal to or more than a predetermined level. As aresult, the AP 300 is capable of determining to switch the connectiontarget of the UE 100 to the eNB 200, without receiving the measurementreport on the eNB 200 from the UE 100.

In this case, description is provided on the assumption that the AP 300decides that a connection target of the UE 100 is switched from the AP300 to the eNB 200.

In step S9103, the AP 300 transmits, to the eNB 200, request informationrequesting to switch to the eNB 200.

In step S9104, the eNB 200 transmits, to the AP 300, in addition to aresponse (Ack) relative to the request information from the AP 300,information (such as contention free and preamble) used for a connectionprocedure to the eNB 200.

In step S9105, the AP 300 transmits, to the UE 100, a switch instructionto switch from the AP 300 to the eNB 200, in response to the receipt ofthe response (Ack) from the eNB 200. The switch instruction includesinformation used in the connection procedure to the eNB 200.

In step S9106, the AP 300 transmits, to the eNB 200, the switchinstruction to the UE 100, and transfers the transmission data addressedto the UE 100.

In steps S9107 to S9109, the UE 100 performs a connection process withthe eNB 200.

Instead of AP 300, a cellular base station that performs communicationsin an unlicensed band may be used in the ninth embodiment.

Other Embodiments

While the present disclosure has been described by way of the foregoingembodiments, as described above, it should not be understood that thestatements and drawings forming a part of this disclosure limit thedisclosure. From this disclosure, a variety of alternate embodiments,examples, and applicable techniques will become apparent to one skilledin the art.

Each of the above-described first embodiment to ninth embodiment may beindividually implemented and implemented in combination of one another.

In each of the above-described embodiments, a case where the eNB 200 andthe AP 300 are a separate device is described; however, the eNB 200 mayinclude a function of the AP 300. That is, the eNB 200 may include aWLAN transceiver. Further, the eNB 400 may include a function of the AP300.

In the above-described embodiments, secure communication between the UE100 and the AP 300 has not been particularly considered; however, suchsecure communication may be considered. The eNB 200 inquires, the UE 100determined to be connected to the AP 300, of the presence or absence ofconnection setting information used in the secure communication with theAP 300. When such connection setting information is not provided in theuser terminal, the eNB 200 requests the AP 300, which is to beconnected, to issue temporary connection setting information. Then, thetemporary connection setting information issued by the AP 300 inresponse to the request from the eNB 200 is notified to the UE 100 fromthe AP 300 via the eNB 200. Detailed procedures will be described,below.

Firstly, the eNB 200 transmits, to the UE 100, WLAN connection settingconfirmation information for inquiring the presence or absence of aconnection setting (secure setting) with the AP 300 that is to beconnected to. The WLAN connection setting confirmation informationincludes an identifier (SSID/ESSID) of the AP 300 to be connected.

Secondly, the UE 100 sends back, to the eNB 200, a WLAN connectionsetting response indicating the presence or absence of the connectionsetting of the inquired AP 300. The WLAN connection setting responseincludes the identifier (SSID/ESSID) of the AP 300 to be connected.

Thirdly, the eNB 200 transmits issuance request information requestingto issue a temporary connection setting, to the AP 300 to be connected,when there is no connection setting in the WLAN connection settingresponse. The issuance request information includes MAC-ID of the WLANof the UE 100.

Fourthly, the AP 300 generates the temporary connection settinginformation in response to the issuance request information from the eNB200, and notifies the eNB 200 of the information. The temporaryconnection setting information includes information on the securesettings (a secure type and a secure key).

Fifthly, the eNB 200 adds the identifier (SSID/ESSID) of the AP 300 tothe temporary connection setting information from the AP 300, andtransfers the same to the UE 100. The eNB 200 may include the temporaryconnection setting information in the above-described scanninginstruction.

In the above-described embodiments, whether the WLAN service isavailable to the UE 100 has not been particularly considered; however,whether the WLAN service is available to the UE 100 may be considered.The eNB 200 inquires a service management server of whether the UE 100connecting to the cell of the eNB 200 is registered in a serviceallowing the use of the AP 300. The eNB 200 may transmit, from the eNB200 to the UE 100, authentication information for registering in theservice when the UE 100 is not registered in that service. Detailedprocedures will be described, below.

Firstly, the eNB 200 transmits, to the service management server,service registration confirmation information for inquiring the presenceor absence of the service registration in a WLAN network. The serviceregistration confirmation information includes an identifier (such asMAC-ID) of the UE 100.

Secondly, the service management server sends back, to the eNB 200,service registration information indicating the registration in the WLANservice. The service registration information includes an identifier(such as MAC-ID) of the UE 100.

Thirdly, the eNB 200 transmits a scanning instruction (WLAN connectionrequest) to the UE 100 when there is a service contract in the serviceregistration information from the service management server. On theother hand, when there is no service contract, the eNB 200 does nottransmit the scanning instruction to the UE 100. Alternatively, the eNB200 decides to provide a temporary service, and transmits, to the UE100, authentication information for a temporary login setting for theservice, that is, a service authentication key (an authentication ID, apassword).

In the above-described embodiments, as one example of the cellularcommunication system, the LTE system is described; however, the presentdisclosure is not limited to the LTE system, and the present disclosuremay be applied to a cellular communication system other than the LTEsystem.

It is described that a white list is a list of connectable APs 300(Planned AP); however, a list of APs 300 to which the UE 100 should notconnect may be added to the white list.

Hereinafter, additional statements of the above-described embodimentswill be described.

[Additional Statement 1]

One of the main objectives of the 3GPP/WLAN interworking study item isto extend the interworking between 3GPP and WLAN beyond the integrationcurrently supported at the CN level. To improve the overall userexperience, further enhancements at the RAN level is needed to achievebetter network utilization, reduce unnecessary UE power consumption andprovide seamless mobility between the two networks. This contributionconsiders some of the scenarios necessary to achieve these objectives.

Based on the study item, the initial phase of the study item is toidentify requirements for RAN level interworking, and clarify thescenarios to be considered in the study while taking into accountexisting standardized. The scenarios considered below will involveenhancements to the current system and the proper UE behaviours shouldbe further analysed.

For 3GPP/WLAN interworking, the operator could consider variousdeployment options. In general, WLAN APs may be deployed in variouslocations. For coverage extension, WLAN may even be deployed in areaswhere 3GPP access networks are not available. However, for 3GPP/WLANinterworking RAN2 should only focus on the scenario where WLAN isoverlaid on the 3GPP system, regardless of whether the WLAN AP isco-located or not with any of the 3GPP nodes.

Observation: 3GPP/WLAN interworking is only applicable for offloadingwhereby WLAN is within coverage of 3GPP systems.

In Release 10 simultaneous network connections to multiple radio accesstechnologies have been enabled by MAPCON, IFOM and non-seamless WLANoffload. To take this into account, the ANDSF framework has beenenhanced with the introduction of Inter System Routing Policies (ISRP),allowing the operator to provide policies based on the traffic exchangedby the UE. In Rel-11, the extensions to ANDSF and Inter-System RoutingPolicies (ISRP) provide to operators a better control of the networkresources used for each application or IP flow. As an example, theoperator may indicate via ANDSF policies that IP flows which require adata rate above a certain threshold are to be sent over a given access.

However, these network enhancements do not address the issue of UE powerconsumption for the purpose of offloading. Offloading provides thenetwork with freed up resources for other UEs that cannot be offloadedto a WLAN AP. Offloading to a WLAN AP is also beneficial when the 3GPPradio or network is congested. Although there are significant advantagesfor offloading from a network's perspective, it should not be necessaryto have both 3GPP radio and WLAN radio turned on at all times since itwill cause excessive power consumption at the UE, esp. if WLAN APs aremore widely deployed. This study item should consider scenarios directedtowards power savings. In particular, an efficient means for WLANdiscovery to prevent the UE from searching for WLAN continuously when noWLAN AP is available to the UE. An efficient WLAN discovery mechanismmay not assume the UE will have its WLAN client turned on at all times.Therefore, the selection of a UE for offloading to WLAN should also becarefully considered depending on the WLAN discovery mechanism.Furthermore, the selection of a candidate UE for offloading to WLANshould not only be based on its relative proximity to a WLAN AP but alsothe appropriateness of the services suitable for WLAN due to backhaullatency.

Proposal 1: To improve UE's energy consumption, an efficient means forWLAN AP discovery should be considered.

For interworking with WLAN, the services that may be suitable foroffloading should be considered. Due to the uncertainly in reliabilityand the potential increased latency associated with the backhaul used bythe WLAN AP, some services e.g., VoIP may not be suitable for offloadingwhereas latency tolerant services would be ideal candidate foroffloading. Therefore RAN2 should consider the UE's connectivity basedon its active services. To have an effective interworking between thetwo systems, UE's behaviour for both inbound mobility to the WLAN andoutbound mobility from the WLAN should be considered. Inbound mobilityto the WLAN may be needed when the 3GPP network decides that the one ormore of the UE's active services should be offloaded to WLAN. AlthoughUE's active services are offloaded to WLAN, it is assumed that the UEwill remain in IDLE on the 3GPP system, e.g., to receive incoming pages.If the UE were to activate a new service that is not suitable for WLAN,RAN2 should consider procedures necessary for outbound mobility fromWLAN to the 3GPP system. RAN2 should further consider whether allservices need to be transferred from the WLAN to the 3GPP system, or ifonly services not applicable for WLAN would be transferred to the 3GPPsystem. UE's power consumption should also be considered if it isnecessary for UE to simultaneously connect with both systems.

Proposal 2: For providing reliable mobility, the UE's behaviour for bothinbound mobility to WLAN and outbound mobility from WLAN should beconsidered.

This additional statement 1 described a few scenarios that should beaddressed in this study item.

[Additional Statement 2]

1. Introduction

As a result of the discussion about how solutions (Solution 1, 2 and 3)can fulfill the requirements, Solution 2 seems to fulfill allrequirements; although there remain a few unclear points, especially asthey relate to ANDSF and RAN rules. This contribution provides furtherexplanation on the differences and how they may be used to meet thetraffic steering requirements. Further details on the fulfilment ofrequirements for Solution 2 are described in the Annex.

2. Discussion

2.1. ANDSF Vs RAN Rules

A few unclear points were described under Solution 2 for fulfillment ofall requirements. Majority of the concerns come from the relationshipbetween ANDSF policy and RAN rules. For example, some concerns come fromthe unpredictability of UE behavior or potential ping-ponging caused byunclear relationship between ANDSF policy and RAN rule. The answers tothe issues below should help to clarify the relationships between ANDSFand RAN rules.

1) If ANDSF is not available, should RAN rules be used?

If ANDSF is not available, RAN should provide rules to ensure consistentbehavior among UEs. Pre-provisioning of UEs with static rules may leadto unpredictable behavior since this is basically up to UEimplementation. This flexibility is one of main advantages with Solution2.

2) If ANDSF is available to the UE, which rule should the UE follow,ANDSF policy, RAN rules or both?

It is currently stated that, “Even if the ANDSF policy is provided tothe UE, RAN has the option to indicate the preferred rule to be used bythe UE”. In principle, the UE should be allowed to use ANDSF if it isavailable to the UE and the UE supports ANDSE However, to prevent anyconfusion, the decision of which rule to use is up to RAN to decide. IfRAN knows that UE has ANDSF available, RAN should allow the UE to useANDSE If we allow the UE to use ANDSF when RAN has informed the UE thatRAN rules should be used then the use of ANDSF would be left to UEimplementation which would prevent uniform behavior among all UEs.Therefore, either the RAN rules or ANDSF policy would be used as decidedby the RAN and not both.

3) If ANDSF is only available to some UEs but not all UEs (maybe someUEs are not ANDSF capable) could the RAN provide its rules only to thoseUEs without ANDSF?

It will be up to the RAN to decide whether to apply RAN rules or ANDSFpolicy. In our view, RAN rule should be provided to all UEs withoutdistinction to avoid any confusion.

4) Do we apply the same rules for roaming UEs? Will the roaming UEs havethe same ANDSF as the non-roaming UEs? Is it necessary for the roamingUEs to behave the same way as the non-roaming UEs?

Again, it will be up to the RAN to decide whether the UE uses RAN ruleor ANDSE Roaming UE's behavior can be predictable for operators if theUE performs traffic steering based on the rule provided by RAN. It isalso good for load balancing.

5) Are there any cases where UE implementation is allowed when the UE isinformed by the RAN to use RAN rules?

Following RAN rules does not imply the UE will automatically scan forWLAN and steer traffic to WLAN. RAN rules assume the UE may also accountfor its battery level status as part of WLAN scanning optimization.Details of WLAN scanning optimization is FFS. For traffic steering fromRAN to WLAN, the UE selects traffic to be steered based on the specifiedDRB within RAN rules. For the selection of traffic to be steered fromWLAN to RAN, the UE may use IFOM if available or UE implementation.

Table 1 summarizes the relationship between RAN rules and ANDSE

TABLE 1 RAN's Rule UE's action UE's action Preference (if ANDSF isAvailable) (if ANDSF is Unavailable) RAN Rules RAN Rules RAN Rules ANDSFPolicy ANDSF Policy UE uses legacy behavior

Based on the above clarifications, we arrived at the followingconclusions:

For Solution 2, RAN decides whether the UE uses RAN rules or ANDSFpolicy.

Proposal 1: If RAN decides that UE should use RAN rules, the UE willonly use RAN rules even if ANDSF is available.

Proposal 2: If RAN decides that UE should use RAN rules, trafficsteering from RAN to WLAN will be according to the traffic informationwhich defines the data bearer selected for offloading.

Proposal 3: For traffic steering from WLAN to RAN, the UE may selecttraffic according to UE implementation or IFOM (if available).

2.2. Clarification on Load Information

In previous discussions, there were suggestions that RAN may indicateits load to the UE in order to trigger the traffic steering from RAN toWLAN. Such an indication has no benefit for operators. For loadbalancing, Solution 2 allows the RAN to adjust thresholds of 3GPP RANRSRP, RSCP, WLAN BSS load and WLAN RSSI to vary the level of offloadingdesired. Additionally, accuracy of access network selection is alsoimproved by using direct metrics rather than indirect metrics such asload information.

Furthermore, Solution 2 can avoid inefficient scanning, traffic steeringusing offloading indication (refer to FIG. 29). If load level increases,RAN promotes network selection by sending an offload indication to theUE. UE initiates network selection using this indication as a trigger.The use of such an offload indicating will prevent any unnecessaryscanning of WLAN esp. in the likely case when users turn off the UE'sWLAN module to conserve power. The UE will only consider turning on theWLAN module if it receives the offload indication.

Proposal 4: For Solution 2, RAN may send an offload indication to informthe UEs of its intention for offloading from RAN to WLAN.

Proposal 5: Even if UE receive the offload indication from RAN, UE hasthe option to determine whether WLAN scanning is preferable based on UEimplementation, e.g., battery level.

The left side of FIG. 29 indicates the case there is no need to performtraffic steering. The right side of FIG. 29 indicates UE initiatesnetwork selection using the offloading indication.

3. Conclusion

This additional statement 2 provides further explanation especially forthe unclear points, describes refinement of Solution 2 and concludes thesolution fulfils all the requirements.

4. Annex

4.1. Evaluation of Requirement Fulfillment

With the above clarfications of ANDSF and RAN rules, it would be ofinterest to reconsider whether Solution 2 satisfies the requirementfulfillments.

Requirement 1:

Solution 2 achieves the proper balance between RAN load and WLAN loadAPs by utilizing ANDSF or RAN rules. In particular, RAN rules willspecify thresholds for 3GPP/WLAN signals and WLAN load to controltraffic steering without explicitly providing RAN's load information.Even if ANDSF were available to the UE, RAN will decide whether ANDSF orRAN rules will be ultilized to avoid any potential conflict between thetwo.

If ANDSF is unavailable to UEs, even with smart UE implementation, thepolicies used by the UEs may be different, so the outcome of theoffloading may still be uncertain. With RAN rules, UE's behaviour ispredictable which leads to predictable offloading control.

Unlike Solution 1, Solution 2 has the advatange that RAN can control thetiming of applying the rules which should result in more accurateoffloading control. For dynamic load control, RAN has the option toadjust thresholds as needed to enable timely access network selection.

Requirement 2:

User experience may be improved by specifying the rule that reflectsRAN/WLAN signal qualities and WLAN load. The RAN specified theresholdsand takes into account of existing 3GPP measurement reports, RAN stateand the relative load generated by the UE so that both user experienceand network performance may be improved.

Since Solution 2 is a UE-based access network selection solution,UE-specific needs such as steering IP flow rather than just DRB can bemore easily fulfilled with less signaling.

Requirement 3:

For improving utilization of WLAN, improving user experience andreduction of battery consumption are needed. From this perspective,Solution 2 satisfies the requirement by allowing the UE to take intoaccount of its battery level, proximity to WLAN and QoS needs to achievethe desired results.

Randomization may be applied to prevent excessive number of UEs fromconnecting to WLAN simultaneously.

Furthermore, offloading indication from RAN may be used to preventunnecessary WLAN scanning. UE initiates this procedure only if theindication is activated.

Requirement 4:

By specifying rules that allows the UE perform WLAN scanning only whencertain RAN conditions are satisfied, battery consumption may bereduced. For instance, by allowing the UE to scan WLAN channel only whenRSRP is less than a certain threshold, UE's power consumption may bereduced.

Requirement 5:

If RAN decides that the UE should use ANDSF, then the traffic steeringmay be based on ANDSE If ANDSF is unavailable and the RAN decides thatthe UE should use RAN rules, the RAN may decide which traffic would beoptimal for offloading to WLAN.

Requirement 6:

Solution 2 does not affect existing 3GPP and WLAN functionalities, sothere is no impact to legacy systems.

Requirement 7:

Solution 2 follows existing WLAN scanning/connection mechanisms, sothere is no impact to IEEE or WFA.

Requirement 8:

RAN may provide to the UE a white list (or black list) consisting ofWLAN service set identifiers so that WLAN system distinction ispossible. It is also possible to provision per SKID-thresholds.

In addition, Solution 2 may also rely on ANDSF to define WLAN specificsystem for offloading. RAN policy may also make use of existing ANDSFpolicy.

Requirement 9:

The fulfillment of this requirement is accomplished through the use ofdedicated signalling for specific UEs.

Requirement 10:

By utilizing randomization (e.g. UE performs random backoff beforetesting whether the target cell is accessible or not) and providing adedicated assistant information (e.g. threshold) for each UE,ping-ponging may be prevented. It is FFS whether additional mechanismsare needed.

[Additional Statement 3]

Rule Example:

-   -   if ANDSF is not available (or not preferred by RAN)        -   if RAN RSRP <x or offloading indicator=yes            -   if WLAN RSSI >y and WLAN BSS load <z                -   offload from RAN to WLAN            -   else if RAN RSRP >x′                -   if WLAN RSSI <y′ or WLAN BSS load >z′                -    offload from WLAN to RAN    -   else forwards the received assistance information to the        interworking upper layer of the UE

Note: Parameters x, x′, y, y′, z, z′ are provided by Network

Splitting Between “if RAN RSRP <x or Offloading Indicator==Yes” and “ifWLAN RSSI >y and WLAN BSS Load <z”

The motivation is UE can allow to be scanning optimization (includingWLAN client off) if RAN RSRP >x and offloading indicator==no or notsignaled. And UE do RAN RSRP measurement regardless scanningoptimization is applied or not.

The Reason Two Thresholds “if RAN RSRP <x” and “OffloadingIndicator==Yes” Having

Even if RAN does not indicate offloading desired, the UE may still wantto scan for WLAN. It's just a way for the RAN to determine how manypotential UEs may not be offloaded (i.e., those UEs with RSRP >x). Thatway the UE may still report WLAN measurements to the eNB, but that theywouldn't be targeted for offloading to WLAN. Sort of like MDT. So thatRAN can refine the adjustment of “x” in the future. This would only beapplicable for dedicated signaling.

The Reason “if WLAN RSSI <y′ or WLAN BSS Load >z′” then UE shouldOffload from WLAN to RAN

It's dangerous the decision offload from WLAN to RAN is up to UEimplementation or ANDSE The important thing here is that the RAN rulescan still be applied to determine if the UE should steer traffic fromWLAN to RAN; however, the selection of traffic to be steered from WLANto RAN will be based on UE implementation. (I.e., If UE applying RANrules move to WLAN, RAN rules should also be used during UE. So UEapplying RAN rules should keep its RAN rules until UE receive updatedparameters (after move back to RAN) to prevent unnecessary ping-pong NWselection. Note Rule preference indicator is included in above “updatedparameters”.

The Necessity of Offload Preference Indicator

Listed parameters are provided by dedicated signaling or broadcastsignaling (More specific, whether all listed parameters are provided bydedicated signaling or there is a possibility that some parameters canbe provided by broadcast signaling.) If there is a situation that RSRPthreshold and WLAN related threshold are provided by broadcast signalwhereas remaining parameters are provided by dedicated signaling, RANshould not change RSRP threshold drastically. Then the Offloadpreference indicator is useful for NW making only UEs located in closeto the WLAN move to WLAN, (if NW knows WLAN and UE's location.)

Of course, there is another possibility that NW send the updatedparameters x, y, z by dedicated signaling instead of Offload preferenceindicator.

To summarize above procedure, UE may obey the rules described in belowtable 2.

TABLE 2 If UE connect to WLAN If UE connect to RAN Assuming RAN RSRP < xN/A if (WLAN RSSI > y and load level isn't Offload WLAN BSS load < z )=> acceptable preference Traffic steering based on RAN indicator == yesrule else => RAN RSRP > x N/A if (WLAN RSSI > y and Offload WLAN BSSload < z) => preference Traffic steering based on RAN indicator == yesrule else => RAN Assuming RAN RSRP < x N/A if (WLAN RSSI > y and loadlevel is Offload WLAN BSS load < z) => acceptable preference Trafficsteering based on RAN indicator == no rule else => RAN RSRP > x N/A RANOffload preference indicator == no RAN RSRP > x′ if (WLAN RSSI < y′ N/Aor WLAN BSS load > z′) => Traffic steering based on UE implementationelse => WLAN RAN RSRP < x′ WLAN N/A

INDUSTRIAL APPLICABILITY

The present disclosure is useful for radio communication fields.

1. A base station included in a cellular radio access network (RAN),comprising: a transmitter configured to transmit, to a user equipment,parameters for an offload from the cellular RAN to a wireless local areanetwork (LAN), wherein the parameters are used by the user equipment toperform an access network selection between the cellular RAN and thewireless LAN, and the parameters include a first threshold to becompared with a cellular signal strength of the cellular RAN, a secondthreshold to be compared with a wireless LAN signal strength of thewireless LAN, and a third threshold to be compared with a load of thewireless LAN.
 2. The base station according to claim 1, wherein when theuser equipment performs the access network selection, the parameterscause the user equipment to perform the offload, in response to thecellular signal strength being lower than the first threshold, thewireless LAN signal strength being higher than the second threshold, andthe load of the wireless LAN being lower than the third threshold.
 3. Amethod performed at a base station included in a cellular radio accessnetwork (RAN), comprising: transmitting, to a user equipment, parametersfor an offload from the cellular RAN to a wireless local area network(LAN), wherein the parameters are used by the user equipment to performan access network selection between the cellular RAN and the wirelessLAN, and the parameters include a first threshold to be compared with acellular signal strength of the cellular RAN, a second threshold to becompared with a wireless LAN signal strength of the wireless LAN, and athird threshold to be compared with a load of the wireless LAN.